Urticaria pigmentosa is characterized by several to many brownish spots that itch and, when scratched, produce welts and reddened skin. The brown spots contain mast cells with high levels of histamine. People sometimes develop generalized flushing and headaches from the massive histamine release from these spots.
Review Date 11/4/2020
Updated by: Elika Hoss, MD, Senior Associate Consultant, Mayo Clinic, Scottsdale, AZ. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.